Routing – loopback ip issue

So I have a weird issue. If I configure a /30 ip on an ethernet interface, for example 10.10.10.1/30 on Router1 and 10.10.10.2/30 on an ethernet interface on Router2, I can ping each other fine…no issues with OSPF (adjacency is formed, etc)

However, if I remove those configs and assign each ip to the loopback0 interface on each router, I'm unable to ping them and no adjacency is formed.

I have OSPF configured and the interfaces are added to area 0. I'm not sure why this is happening. If you need any configs/output from me, please let me know.

Router 1 - with private ip configured on ethernet interface as ptp link comes up fine.
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#sho ip ospf neighbor

Port          Address         Pri State      Neigh Address   Neigh ID        Ev
8/21-8/22     10.10.10.1      1   FULL/OTHER 10.10.10.2      10.10.10.2    5

ethernet 8/21-8/22,OSPF enabled
     IP Address 10.10.10.1, Area 0
     OSPF state ptr2ptr, Pri 1, Cost 1, Options 2, Type pt-2-pt Events 3

Router 2
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#sh ip ospf neighbor

Port        Address         Pri State      Neigh Address   Neigh ID        Ev
5/1-5/2     10.10.10.2      1   FULL/OTHER 10.10.10.1      10.10.10.1    14

If I switch to the loopbacks with the publicly routable ip, here is the output:

Router 1
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No ospf neighbor formation

lb2,OSPF enabled
     IP Address 111.111.111.1, Area 0
     OSPF state DR, Pri 1, Cost 0, Options 2, Type broadcast Events 5
     Timers(sec): Transit 1, Retrans 5, Hello 10, Dead 40
     DR:  Router ID 111.111.111.1      Interface Address 111.111.111.1
     BDR: Router ID 0.0.0.0           Interface Address 0.0.0.0
     Neighbor Count = 0, Adjacent Neighbor Count= 0

#sh ip route 111.111.111.0
Total number of IP routes: 262007, avail: 137 (out of max 262144)
        Destination     NetMask         Gateway         Port       Cost   Type
        111.111.111.0    255.255.255.252 0.0.0.0         lb2        1      D

Router 2
--------
No ospf neighbor formation

lb1,OSPF enabled
     IP Address 111.111.111.2, Area 0
     OSPF state DR, Pri 1, Cost 0, Options 2, Type broadcast Events 11
     Timers(sec): Transit 1, Retrans 5, Hello 10, Dead 40
     DR:  Router ID 111.111.111.2      Interface Address 111.111.111.2
     BDR: Router ID 0.0.0.0           Interface Address 0.0.0.0
     Neighbor Count = 0, Adjacent Neighbor Count= 0

#sh ip route 111.111.111.0
Total number of IP routes: 262119, avail: 21 (out of max 262144)
        Destination     NetMask         Gateway         Port       Cost   Type
        111.111.111.0    255.255.255.252 0.0.0.0         lb1        1      D